Accessibility improvements for carousel

[compulim]

Is your feature request related to a problem?

It is not trivial to control the carousel inside the message.

Describe the suggestion or request in detail

I have talked to accessibility team, and they suggest:

1. Take flipper out of focus ring (i.e. set tabindex="-1")
2. Add CTRL + LEFT/RIGHT to mimic the flipper button click (scroll left/right)
3. Add CTRL + LEFT/RIGHT to keyboard help screen to educate PWD how to scroll inside the carousel

Describe alternatives you have considered

No response

Additional context

No response